This invention relates to a method of recovering elemental phosphorus from phosphorus sludge. In particular, it relates to such a method where the sludge is melted, an oxidizing agent and water are added, and the sludge is stirred to coalesce phosphorus globules into a pure phosphorus continuous phase which separates from the dirt in the sludge.
Elemental phosphorus can be made by heating phosphate rock, carbon, and sand in an electric furnace. Phosphorus vapors given off in the furnace contain solid impurities, such as slag, phosphate rock, sand, and coke, which cause the formation of sludge when the phosphorus vapors are condensed to the liquid form. Gradually, phosphorus sludge accumulates on top of this liquid phosphorus layer.
Phosphorus sludge is often stored in outdoor ponds. Periodically, it is necessary to reduce the amount of stored sludge either by recovering phosphorus or by converting the sludge into useful products. Such treatment may require the separation of phosphorus from the impurities.
In U.S. Pat. Nos. 3,436,184 and 3,515,515 there is described a process for reducing the phosphorus content of phosphorus sludge by adding chromic acid to the sludge. That process removes only a portion of the phosphorus in the sludge.